Shale Reservoirs: Improved Production from Stimulation of Sweet Spots* Khaled H. Hashmy1 and Ashok Bhatnagar1 Search and Discovery Article #41355 (2014)** Posted May 31, 2014

*Adapted from oral presentation given at GTW-AAPG/STGS Eagle Ford plus Adjacent Plays and Extensions Workshop, San Antonio, Texas, February 24-26, 2014 **AAPG©2014 Serial rights given by author. For all other rights contact author directly. 1

Weatherford International Ltd., Houston, TX ([email protected])

Abstract Recently introduced azimuthal LWD measurements combined with well-site measurement of parameters on drill cuttings have proven to be a game changer in the quest for improved productivity in laterals drilled in shale reservoirs. While Pyrolysis, XRF, and XRD measurements on drill cuttings at the well site provide mineralogical and organic content information in near real-time, of particular interest are the LWD Azimuthal Spectral Gamma Ray and the LWD Azimuthal Sonic devices, both of which gather data in sixteen azimuthally-fixed bins. The LWD Azimuthal Spectral Gamma Ray furnishes clay types and identifies zones with high TOC based on the response of the uranium measurement. A unipole configuration with a single, directionally focused transmitter and one array of six directional receivers that are azimuthally aligned with the transmitter is used in the LWD Azimuthal Sonic device. The azimuthally focused sensors can differentiate the slowness of the refracted compressional and shear waves emanating from different azimuthal directions around the borehole. The sonic waveforms received in 16 azimuthally fixed-orientation bins are processed to yield 16 independent, azimuthally oriented compressional and refracted shear slowness curves, which in turn, combined with the LWD density, provide 16 curves of Young’s Modulus, Poisson’s Ratio and rock Brittleness Index, each of which can also be used to generate the corresponding 360° borehole image along the length of the lateral. The combination of mineralogy, abundance of organic material and accurate brittleness coefficient along the length of the lateral is often sufficient to define the sweet spots that exhibit enhanced reservoir properties and are amenable to stimulation and fracturing. The LWD Azimuthal Sonic in horizontal wells provides compressional and shear slowness in the vertical and horizontal directions, and as is common in anisotropic shale reservoirs, the shear velocity in the horizontal plane is often greater than that in the vertical plane. Combined with the crossdipole measurements in a vertical well, an accurate orthorhombic velocity model may be generated. This will lead to greater precision in tracing the topography of the shale pay on the seismic section and hence lead to more precise definition of the well trajectory. This will facilitate in confining the well path to the targeted pay zone. Not the least of the benefits of determining the shear anisotropy is that it could be factored into the stimulation design to achieve more effective hydraulic fracturing.

Selected References Abou-Sayed, I.S., M.A. Sorrell, R.A. Foster, E.L. Atwood, and D.R. Youngblood, 2011, Haynesville Shale Development Program from Vertical to Horizontal: SPE North American Unconventional Gas Conference and Exhibition, The Woodlands, Texas, 14-16 June, 2011, SPE 144-425. Basu, N., G. Barzola, H. Bello, P. Clarke, and O. Viloria, 2012, Eagle Ford Reservoir Characterization from Multisource Data Integration: Search and Discovery Article #80234, Web accessed May 9, 2014. http://www.searchanddiscovery.com/documents/2012/80234basu/ndx_basu.pdf Hall, J.D., 2011, Pioneer Natural Resources Presentation: Tight-Oil - Eagle Ford 2011 Conference, Houston, Texas, August 30, 2011, unpublished. Hashmy, K.H., S. Abueita, C. Barnett, and J. Jonkers, 2011, Log Based Identification of Sweet Spots for Effective Fracs in Shale Reservoirs: Canadian Unconventional Resources Conference, Calgary, Alberta, Canada, 15-17 November, 2011, CSUG/SPE SPE149278. Hashmy, K.H., D. Tonner, S. Abueita, and J. Jonkers, 2012, Shale Reservoirs: Improved Production from Stimulation of Sweet Spots: SPE Asia Pacific Oil and Gas Conference and Exhibition, Perth, Australia, 22-24 October, 2012, SPE158881. Mickael, M., C. Barnett, and M.S. Diab, 2012, Shear Wave Anisotropy Measurement from Azimuthally Focused LWD Sonic Tool: SPE 162175, DOI: http://dx.doi.org/10.2118/162175-MS. Pope, C., 2012, Improving Completion and Stimulation Effectiveness in the Eagle Ford Shale: SPE Eagle Ford Shale Workshop, 21-23 August 2012, San Antonio, Texas. Tonner, D., K.H. Hashmy, S. Abueita, and J. Jonkers, 2012, Focusing Stimulation Efforts on Sweet Spots in Shale Reservoirs for Enhanced Productivity: Search and Discovery Article #41110, Web accessed May 9, 2014, http://www.searchanddiscovery.com/pdfz/documents/2012/41110tonner/ndx_tonner.pdf.html.

Shale Reservoirs: Improved Production from Stimulation of Sweet Spots Khaled H. Hashmy, Weatherford Petroleum Consulting, Houston, TX Ashok Bhatnagar, Weatherford Petroleum Consulting, Houston, TX

AAPG/STGS Eagle Ford plus Adjacent Plays & Extensions Workshop 24-26 February 2014 | San Antonio, Texas

1.

2.

Frac Stages are often placed at arbitrary spacings along the Lateral WITHOUT considering the variations in rock and reservoir properties. Safety, cost and time considerations sometimes impel operators to minimize studies in laterals

STUDIES HAVE SHOWN THAT: 1.

UPTO 21% OF PERFORATION CLUSTERS ARE NOT CONTRIBUTING 2. 30% TO 43% OF THE PERFORATION CLUSTERS CONTRIBUTE LESS THAN 1% OF TOTAL PRODUCTION 3. ONE OF THE PROBABLE CAUSES COULD BE PLACEMENT OF PERFORATION CLUSTERS IN ZONES WITH POOR RESERVOIR QUALITIES

 Measurements

on Drilling Fluids and Rock Cuttings offer Approach for Sweet Spot Identification • Advanced Mud Gas Extraction/Detection • Cuttings Analysis  X-Ray Fluorescence, X-Ray Diffraction & Pyrolysis 1. 2.

 Logging

In Pilot Holes In Laterals

While Drilling  Wireline Logging  Seismic

•C1-C8 •Benzene •Toluene •Ethane •N2 •CO2 •55 Sec. •Gas In/Out

Delineates top and bottom of the reservoir Identifies changes in fluid type Can optimize downhole fluid sampling

•

Critical fluid properties can be predicted directly from mud gas sample

•

Need good calibration data set and good mathematical models Tonner et al., AAPG ICE 2012

Track 4: Increased Total Hydrocarbon Track 5: Separation C1 and Balance Ratio Track 6: Increased Gas to Liquids Ratio Track 7: Crossover HC and ARO/ALK

HC & Aro/Alk

Fluid Saturation

C1/ROP

Wetness & Balance

C1/C2

Methane Content %

THC%

Wellpath

ROP GR

•

Total Hydrocarbon Content (THC%) identifies the Zones of Interest which results in increased efficiency during completions planning.

•

Fluid indicators (C1%, C1/C2, HC & ARO/ALK & Wetness/Balance) help in characterizing the Hydrocarbon fluid type.

•

Gas components & ratios also provides an insight into the petrophysical properties (Porosity & Permeability).

•

Fluid saturation differentiates between a Hydrocarbon saturated & Water Saturated.

ZA

ZC

ZD

Zone from Light Oil to

Presence of Hydrocarbon

ZB

Hydrocarbon Saturation in the EF

Transition

Very Light Oil/Condensa tes at approx. 0000 ft MD

XRD, XRF AND PYROLYSIS MEASUREMENTS ON DRILL CUTTINGS IN NEAR REAL TIME

1. 2.

3. 4.

Commence with XRD/XRF and Pyrolysis on Pilot vertical holes and laterals. Establish proxies for TOC with Trace Elements. Resolve Mineralogy from the elemental data set. As uncertainty is reduced move to XRF only.

Benchtop when compared to hand held device provided greater range of elements and superior accuracy and precision • XRF measures 10-12 Major Elements (oxide wt.%) SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 (plus S and Cl for most lithologies)

• XRF measures 18 Trace Elements (ppm) V Cr Co Ni Zn Ga As Br Rb Sr Y Zr Nb Mo Ba Hf Th U

• Many minerals show considerable variability in their elemental composition, particularly with regard to trace elements.

Tonner et al., AAPG ICE 2012

Shale Well B Scale : 1:1000

Ele me ntalGR Fe 2O3 Al2O3 180 0 % 60 % 25 0 GRC WFFE WFAL Ele me ntal Units 0 API 180 0 - 0.06 0 - 0.25 0 0

Unit 7-1

Unit 6-3

Unit 6-2

Unit 6-1

Package 5

Unit 4-2 Unit 4-1 Unit 3-4 Unit 3-3 Unit 3-2 Unit 3-1

Package 2

Package 1

Package 0

Package Z

K2O % KC

M gO SiO2 CaO TIO2 % 3 0 % 60 0 % 50 0.2 % 0.9 0 WFM G NA2O P2O5 M nO WFSI WFCA WFTI 30 0.03 0.5 % 2.5 0 %0.65 0.01 %0.06 0 - 0.6 0 - 0.5 0 -0.006 0 30

SO3 50 WFS -0.018 0

Th ppm 15 0 THC 15 0

U ppm 10 UC 10

Pilot well: XRF COMBINED with Enhanced Gas Measurements Identify the “Sweet Spot”

Hashmy et al., 2012

Wellbore maintained +/- 10 feet above target in dipping beds

AAbou-Sayed et al., 2011

Unipole configuration used with a single, directionally focused, transmitter and one array of six directional receivers which are azimuthally aligned with the transmitter

X-Y Magnetometers track the azimuthal orientation as the drill string rotates. Differentiates P & S from different azimuthal directions

CrossWave Azimuthal Sonic Data Acquisition As the tool rotates, X- and Y-axis magnetometers track the orientation of the transducers.

16 15

Over a 30 second acquisition cycle, 210 azimuthally-oriented waveform sets are acquired and sorted into 16 azimuthal bins to facilitate analysis of shear wave anisotropy.

(Standard real-time DTC and DTS are available every 10 seconds.)

1 2

14

3

13

4

12

5 6

11 10

9

8

7

 AZIMUTHAL

SHEAR NOT SIGNIFICANTLY DSIPERSSIVE: • FREQUENCY DEPENDENT DISPERSSION

CORRECTION NOT NEEDED • BOREHOLE DEPENDENT DISPERSSION CORRECTION NOT NEEDED 

CENTERING OF LWD AZIMUTHAL SONIC IN BOREHOLE IS NOT A PROBLEM AS FOR WIRELINE CROSSED DIPOLE DEVICE.

 SHEAR

MEASUREMENT IS ONLY AVAILABLE WHEN FORMATION SHEAR VELOCITY IS FASTER THAN THE COMPRESSIONAL VELOCITY IN THR BOREHOLE FLUID  HIGH TRANSMITTER FREQUENCY RESULTS IN FAIRLY SHALLOW DEPTH OF INVESTIGATION

 LWD

AZIMUTHAL GR, DENSITY & UNIPOLE SONIC TRANSDUCERS SCAN 360o IN EACH DRILL STRING ROTATION  MEASUREMENTS STORED IN 16 BINS  SPECTRAL GR, DENSITY & UNIPOLE SONIC IMAGES GENERATED FOR THE LATERAL

Combined

With Wireline Crossed-dipole Data from the Pilot Hole, the Azimuthal LWD Sonic Furnishes an Accurate 3-D Velocity Model for Compressional and Shear Waves This is Used to Correct and Upgrade the Seismic Interpretation and Helps in Establishing Seismic Attributes

Eagle Ford Reservoir Characterization from Multisource Data Integration*N. Basu1, G. Barzola1, H. Bello1, P. Clarke1 and O. Viloria1 Search and Discovery Article #80234 (2012)

a) 16 Radially spaced P & S Measurements

and corresponding Images along the lateral b) 16 Radially spaced E and μ computations and corresponding Images along the lateral c) 16 Radially spaced computations of Brittleness and corresponding image along the lateral

Brittleness Image

Poisson’s Ratio

Young Modulus Image Density Image

Anisotropy

DTs Image

DTc Image

29

360o Rock Properties Imaging

13ADU9 - SPE WORKSHOP: Addressing the Petrophysical Challenges Relevant to Middle East Reservoirs

 GEOMECHANICAL

DATA ALONG LATERAL LEADS TO COST SAVINGS THROUGH SELECTIVE STIMULATION

 PROVIDES

GEOLOGICAL & PETROPHYSICAL DATA FOR UNDERSTANDING FACTORS CONTROLLING VARIATION IN RATES FROM STAGE TO STAGE

 Hydraulic

frac stage placement based on sweet

spots will - Eliminate fracking into poor reservoir intervals and concentrate on the Sweet Spots - Help in the design of proper frac parameters - Optimize frac efficiency and proppant placement. - Ultimately all of the above will lead to reduced completion cost

 Many

approaches for sweet spot identification are available to optimizing fracs  GC Tracer, XRF/XRD & Pyrolysis on cuttings offer a rapid, near real time approach for mineralogy and hydrocarbon identification  LWD Azimuthal SGR & Sonic provide real time data on TOC and Anisotropy